Vane for an axial ventilator and method for producing the same



Jan. 24, 1967 EYH LD ET AL 3,300,123

VANE FOR AN AXIAL VENTILATOR AND METHOD FOR PRODUCING THE SAME Filed May24, 1965 United States Patent 3,300,123 VANE FOR AN AXIAL VENTILATOR ANDMETHOD FOR PRODUCING THE SAME Helmut Freyholdt and Alfred Aebischer,Stafa, Zurich, Switzerland, assignors to Ventilator A.-G., Stafa,Switzerland Filed May 24, 1965, Ser. No. 458,341 Claims priority,application Switzerland, May 29, 1964, 7,012/ 64 Claims. (Cl. 230-434)The present invention has reference to an improved sheet metal blade orvane for axial blowers and to a new and improved method for theproduction of such vane.

Although the use of sheet metal vanes is known for wall ventilators andalso for tubular axial blowers, in such instance there was only usedsheet iron or steel with relatively thick walls in order to enablewelding of the vane to the steel hub of the ventilator. Even though aconsiderable reduction of the weight of the vanes and thus the weight ofthe impeller provides important advantages it has been found that thinwall sheet steel causes great difiiculties during welding to the steelhub of the impeller and, furthermore, has the tendency to distort.Likewise, the use of aluminium sheet for this purpose has not proven tobe satisfactory since with the welding of aluminium a week locationappears at the welding seam.

Accordingly, it is a primary object of the present invention to providean improved construction of vane or blade for axial blowers or the likeoperating at relatively high pressures and high rotational speeds whichenables the use of thin wall sheets, particularly aluminium sheets.

A further important object of this invention has reference to animproved method of manufacturing vanes for use with axial ventilatorsand the like.

Another specific object of this invention concerns itself with theconstruction of an improved blade or vane for fluid-flow machinery, suchas axial ventilators, which is relatively easy and inexpensive tomanufacture, provides good operating efiiciency, is simple to mount tothe hub of the impeller, even can b repositioned after mounting.

The vane or blade designed according to the teachings of the presentinvention generally comprises a folded sheet strip and exhibits a vaneportion and a flexed, slightly arched i.e. slightly convexed baseportion. It is to be understood that the inventive blade can be used forpractically all ventilators, for instance wall ventilators.

The method of the invention for the manufacture of a sheet metal vane isgenerally characterized by the features that a sheet metal strip is cutsubstantially trapezoidal and stamped or otherwise formed into a twistedvane, at the wide end of the vane there is formed a base portion whichis flexed at approximately right-angles to the vane proper. This baseportion is then formed so as to possess a slightly arched configuration,i.e. is slightly convex, and the fold edge between vane portion and baseportion defines the transition from a substantially cylindrical surfaceinto a partial sphere or spherical shell.

By virtue of the inventive vane or blade construction it is possible todispense with welding of the vane to the impeller hub, and, for example,to use a screw connection. Consequently, it is possible to use thin wallsheet metal e.g. aluminium as material for forming the inventive vanes.

Use of a screw connection enables adjustment and subsequentlyre-positioning of the inlet or approach angle of the blade. Due to thispossibility there is effectively overcome a major disadvantage ofprevious sheet metal vanes, namely impossibility of subsequentlyaccommodating their approach angle to momentarily encountered operatingconditions. This possibility of re-positioning is subordinate forso-called profiled vanes since in con- "ice trast with sheet vanesdeviations of the output from the rated value does not bring aboutimportant disadvantages for a large efliciency range. Previously, asheet metal vane or blade was only practically as aerodynamicallyefficient as a profiled vane in the so-called optimum point. However,the present invention renders it possible to provide a new and improvedsheet vane possessing all of the advantages of the profiled vane and thesheet vane and still further advantages, and at the same time does notpossess all essential disadvantages of both these type vanes.

Other features, objects and advantages of the invention will becomeapparent by reference to the following detailed description and drawingin which:

FIGURE 1 is a perspective view of an impeller designed according to theteachings of the present invention wherein one vane has been removed tofacilitate illustration of details of the impeller hub; and

FIGURE 2 is a perspective view of a new and improved impeller vanedesigned according to the invention.

Describing now the drawing, by referring to FIGURE 1 it will be seenthat the individual sheet or sheet metal vanes 1 are screw-connected orthreaded for instance with a spherical-shaped impeller hub 2. Eachinventive impeller vane 1 is composed of a thin-walled, bent sheet stripand possesses a twisted vane portion 3 and an arched e.g. slightlyconvex, flexed base portion 4 appropriately accommodated to the outersurface 2a of the impeller hub 2. It will be further observed that thisbase portion 4 exhibits a centering hole 5 arranged at the axis SSpassing through the center of gravity of the vane portion 3. A pivotbolt 15 or equivalent structure, conveniently shown in phantom lines inFIGURE 2, is receivable in the centering 'hole 5 and engages with acentering hole 8 (FIGURE 1) provided at the impeller hub 2. Base portion4 also is seen to possess two further apertures or holes 6 and 7. Inaddition to a centering hole 8 provided at the impeller hub 2 at thelocation of attachment of each vane 1 there is further provided twoarcuate-shaped slots 9, 10, typically kidney-shaped, through each ofwhich there piercingly extends a respective connecting screw 11 and 12passing through the holes 6 and 7 respectively of the base portion 4. Tocomplete the connection non-illustrated nuts are threaded at the innersurface of the impeller hub 2 to the screws 11 and 12.

Since the pressed or stamped hollow substantially spherical-shaped baseportion 4 of each vane 1 exhibits an internal radius corresponding tothe outer'radius of the impeller hub 2, the vane 1, specifically itsbase por- 7 tion 4 snugly bears against the hub 2 in any given position.Such also permits adjustment of the angular position of the vane 1 aboutits prescribed axis of rotation, and with the aid of the slots 8 and 9and the screws 11 and 12 respectively the desired position at the hub 2is fixed. As previously mentioned each vane 1 is provided with a pivotpin 15 arranged in the centering hole 5 and extending out of the baseportion 4 for engagement with a centering hole 8 of the hub 2, tothereby permit turning of the relevant vane 1 about its center ofgravity axis SS.

The previously described vane construction permits the use of thin sheetand the use of aluminium as the material for the vanes due to dispensingwith a welding operation and by utilizing a screw-connection. As aresult, there is provided a considerable saving in weight in contrastment of the vanes.

Furthermore, the use of aluminium sheet enables production of impellerswhich are corrosion resistant, and the vanes need not be provided with acostly protective layer safeguarding against corrosion as was previouslythe case. Moreover, the use of a simple screw connection in place ofcumbersome welding of the vanes brings about considerable saving incosts and the time for mounting, so that no skilled labor is required.

Due ot the relatively light weight of the inventive vane relativelysmall centrifugal forces appear at the impeller, so that the impellerhub can likewise be constructed of lighter weight than was previouslythe case. Hence, the overall construction including shaft, bearings,housing and foundation can be made lighter, thereby bringing about afurther saving in cost.

Moreover, by using thin-walled sheets there are obtained considerablythinner discharge edges at the vanes, so that reduced tunbulence at suchlocation results in better efficiencies and less noise than previously.It need not be particularly stressed that both these factors play animportant role in ventilators. There is still further mentioned that theinvention provides an improvement of fiow conditions at the inlet edgeof the vane due to the use of thin-walled sheets.

The inventive vane is considerably lighter than the known profiled vaneseither cast or machined as solid bodies. This is likewise true for vanesformed of plastic, wood or other non-metallic materials.

A further advantage of the inventive sheet metal vane in comparison withknown profiled vanes is the smoothness of its surface. While with knownprofiled vanes it is only possible to obtain a smooth surface by asubsequent costly treatment, for instance by polishing, the inventivevane makes it possible to even obtain a mirrorsmooth surface by properselection of the vane sheet metal, and, thus, there can be obtained avane with better efiiciency without additional processing.

In addition to a surface treatment the cast vanes constructed asprofiled solid bodies require an extensive aftertreatment, among otherthings threading has to be cut for the attachment bolts, the vane edgesat the inside and outside have to be exactly faced, and the axis ofrotation has to be determined. In contradistinction, the inventive vanedoes not require any after-treating steps, resulting in a considerablesaving in cost.

A further disadvantage of the cast profiled vanes not present with theinventive vane is the irregularity in the vane weight which unfavorablyaffects balancing, so that mounting of the impeller requires a greatdeal of time and effort. Due to the uniformity in weight of theinventive sheet vane mounting at the impeller is considerablysimplified.

Since the inventive vane has its axis of rotation coinciding with thecenter of gravity axis turning of the vane does not result in anyshifting of the center of gravity. This provides a considerableadvantage since changing of the vane angle is possible without requiringsubsequent balancing. With most of the cast, profiled vanes generallyused in ventilators the axis of the attachment bolts does not coincidewith the center of gravity axis of the vane, so that upon rotating thevane there is produced a new imbalance. Since balancing of the impellerusually entails returning it to the manufacturer-not possible in manycasesthere is generally foregone any re-adjust- Thus, the possibility ofaccommodating the vane angle to momentarily encountered operatingconditions becomes illusory and these profiled vanes are practicallyused as rigidly mounted vanes.

It is further mentioned that with certain special vane construction foraxial ventilators or turbines it is known to have the axis of rotationcoincide with the axis of the center of gravity, whereby however, itmust be underscored that in so doing certain technical difiiculties andconsiderable increase in cost is associated therewith. Rotating the vaneabout its center of gravity axis is possible 4. in the present instancewithout increased costs due to the inventive construction incorporatinga lateral base portion against which bear externally of the rotationalaxis of the vane the attachment screws. With the exception of certainvery expensive casting processes there are no casting processes forprofiled vanes which result in such a uni formly cast vane that thetheoretical center of gravity axis coincides with the actual center ofgravity axis. On the other hand, the inventive light-weight sheet metalvane for the first time renders it possible to bring into coincidence,in the most simple manner, the rotational axis and the center of gravityaxis.

Furthermore, by referring to FIGURE 1 it will be recognized that it ispossible without any considerable further cost to provide an angleadjustment scale 16 at the base portion 4 of the vane 1 which cooperateswith a, marking 17 located at the impeller hub 2 in order to facilitateadjustment of the angle of attack of the vane 1. Consequently, theflexed base portion 4 not only permits turning of the vane 1 withconstant position of its center of gravity, rather also very simple andexact adjustment of its position.

The good hearing or contact of the base portion 4 of the inventive vane1 with the impeller hub 2 further provides tight sealing, this not beingpreviously possible with rotatable profiled vanes without difiiculty.Air-tight sealing between vane 1 and impeller hub 2 provides higherefficiency and reduced air noise.

It is further mentioned that the hollow partial sphereshaped or archedbase portion 4 constructed as an integral Component of the vane 1strengthens this vane at the zone most subjected to load. The fold edgeor line 18 of the base portion 4 to a certain extent provides thetransition of one partial sphere into a second partial sphere, so thateven with relatively thin sheets there is imparted to this edge aparticularly high strength and stiffness, Due to this substantiallyconvex or spherical-shaped configuration of the base portion 4 of thevane 1 tensile and bending loads can be transmitted up to bothconnecting screws 11, 12 without deformation of base portion 4. Sincethe strongly curved base portions 4 are fixedly screwed to the region ofthe impeller hub 2 most subjected to load and serve as reinforcement ofthe hub it is possible to use a light-weight impeller construction.

It is important for ventilator impellers to maintain a uniform impellergap between the tips of the vanes and the ventilator housing in orderthat the efficiency is not impaired. Therefore, the spacing of all bladeor vane tips from the axis of the impeller must be held within verynarrow limits. In prior art impellers having heavy profiled vanes, thetips of the vanes were milled after the vanes were mounted upon theimpeller hub. This expensive operation, for instance milling or grindingof the vane tips, up to the present was avoided with rigid sheet metalvanes, firstly, because such was associated with difficulties, andsecondly, because the opinion prevailed that sheet metal vanes at anyrate were cheap alternatives having poor efficiency.

Since the inventive vane construction should at least be equallyeflicient in all respects to all previous. constructions, a uniformimpeller gap can be obtained if from the start all vanes are formedsomewhat short, whereby during mounting the vanes can be brought to thedesired external diameter of the impeller by using underlays or supportsformed of thin foils or sheets. This renders it possible tosatisfactorily avoid subsequent working of the vane tips.

In order to ensure against any displacement of the rotational axisduring turning of the vane, particularly with impellers rotating at highspeeds, each base portion 4 of the vane 1 can be provided with thepreviously considered pin 15 engaging in an associated guide hole 8provided at the impeller hub 2, such pin serving as pivot shaft or axisfor the vane.

To simplify cutting of the sheet metal vane from a strip of sheet and tomake the punching or stamp-ing tools necessary for such work cheaper,the present invention contemplates cutting a sheet metal strip intotrapezoidal shape. Moreover, according to the invention, this sheetmetal strip is pressed or otherwise formed into a twisted vane and atits wide end there is flexed at approximately right angles to thetwisted vane portion the base portion 4. The latter is formed so as tobe slightly convex, whereby the fold line or edge 18 between vaneportion 3 and base portion 4 forms the transition of a substantiallycylindrical generated surface int-o a substantially partial sphere. As aresult, aerodynamic design of the sheet metal vanes is such that bothlengthwise edges of the cut vane are linear.

Although in most instances it would be desirable to provide the impellerwith tan inflow hood to increase the efficiency, this expedient haspreviously been dispensed with since such hood must be separatelymanufactured and subsequently connected with the ventilator housing.These additional costs could not be readily justified.

However, since the impeller hub 2 of the inventive axial ventilator canbe manufactured of sheet metal it is possible to construct this impellerhub 2 in such a manner that its forward portion 2b is eflective as aninflow hood, so that without any considerable increased cost there isobtained a combined impeller hub and inflow hood 2, 212 respectively.

With previously known impellers the impeller hub is generally broken offinto a sharp edge at the outflow side so that formation of turbulenceand noise could not be prevented at this location. Furthermore, withsuch known constructions it was not possible to reverse the flowdirection with respect to the impeller hub since the subsequentapplication of an inflow hood at the original outflow side was notpossible due to a lack of space.

On the other hand, with the inventive ventilator it is possible toaerodynamically configure the impeller hub 2 at both sides. Since thereis likewise formed a bent-over collar, generally designated by referencecharacter 2c, at the outflow side of the hub 2 there is not onlyobtained an aerodynamically favor-able impeller construction usable inboth flow directions, rather also an additional stiffening of such hub.

It is still further to be mentioned that the hollow spherical-shapedimpeller hub 2 permits simple application of the balancing weights fromone side both in the forward and also rea-r balancing planes, so thatthe impeller does not have to be removed from the balancing machine, aswas previously the case, in order to be able to apply the balancingweights to the side facing the machine. To this end, the impeller hubcould be provided with a marking edge for the forward balancing plane.Furthermore, the hollow spherical-shaped hub 2 enables adhesiveapplication of the balancing weights 1'9; previously such always had tobe either screwed or welded. Adhesive application of the weights 19which is both simpler and cheaper is possible with the inventiveconstruction of impeller hub 2 because no danger exists that withpossible failure of the adhesive material the weights can be propelledaway during the balancing operation itself or after. wards. In contrastwith previous impeller hub shapes the 6 hollow spherical-shaped hubalways retains the balancing weights within its region.

While there is shown and described present preferred embodiment of theinvention it is to be distinctly understood that the invention is notlimited thereto but may be otherwise variously embodied and practisedwithin the scope of the following claims.

What is claimed is:

1. In combination, an axial flow impeller having an annular hub with anouter spherical shaped surface portion, a plurality of vane meansmounted on the spherical shaped hub portion, each vane means comprisinga folded sheet metal strip incorporating a vane portion and a baseportion, said base portion having a substantially spherical shapedsurface corresponding to that of said spherical shaped surface portion,means adjustably securing the base portion of said vanes to thespherical shaped surface portion, said means comprising a centralcentering means and a pair of clamp fasteners engaging slots in thespherical shaped hub surface portion whereby said vane means on therelease of the securing means may be pivoted about the central centeringmeans.

2. The combination defined in claim 1, wherein the inner opposed surfaceof said annular hub is also spherical shaped; and including balancingweights cemented to said inner opposed surface.

3. The combination defined in claim 1, wherein said centering means is apivot pin on said base portion and an opening in said spherical shapedsurface portion for accepting said pin.

4. The combination defined in claim 1 wherein each base portion isprovided with a scale for adjusting the angular position of said vanemeans at the impeller hub, said spherical shaped surface portion beingprovided with a respective surface marking cooperating with said scaleof the associated vane means.

5. The combination defined in claim 1 wherein said impeller hub isprovided with an inflow hood in front of said plurality of vane meansand an outflow collar behind said plurality of vane means.

References Cited by the Examiner UNITED STATES PATENTS 525,928 9/1894Thompson 230134 984,812 2/1911 Hearst 230134 1,476,137 12/1923 Bilan230- 1,603,076 10/1926 Hanson 29-156.8 2,915,238 12/1959 Szydlowski230134 2,985,952 5/1961 Nutter et a1 29l56.8 3,085,632 4/1963 Schwegler-l67 3,201,857 8/1965 Klonoski 29156.8

FOREIGN PATENTS 1,121,516 5/1956 France.

949,899 9/1956 Germany.

167,581 2/ 1921 Great Britain.

631,231 10/ 1949 Great Britain.

702,312 1/1954 Great Britain.

DONLEY J. STOCKING, Primary Examiner.

HENRY F. RADUAZO, Examiner,

1. IN COMBINATION, AN AXIAL FLOW IMPELLER HAVING AN ANNULAR HUB WITH ANOUTER SPHERICAL SHAPED SURFACE PORTION, A PLURALITY OF VANE MEANSMOUNTED ON THE SPHERICAL SHAPED HUB PORTION, EACH VANE MEANS COMPRISINGA FOLDED SHEET METAL STRIP INCORPORATING A VANE PORTION AND A BASEPORTION, SAID BASE PORTION HAVING A SUBSTANTIALLY SPHERICAL SHAPEDSURFACE CORRESPONDING TO THAT OF SAID SPHERICAL SHAPED SURFACE PORTION,MEANS ADJUSTABLY SECURING THE BASE PORTION OF SAID VANES TO THESPHERICAL SHAPED SURFACE PORTION, SAID MEANS COMPRISING A CENTRALCENTERING MEANS AND A PAIR OF CLAMP FASTENERS ENGAGING SLOTS IN THESPHERICAL SHAPED HUB SURFACE PORTION WHEREBY SAID VANE MEANS ON THERELEASE OF THE SECURING MEANS MAY BE PIVOTED ABOUT THE CENTRAL CENTERINGMEANS.